Thermal Optimization of Injection Molds Produced by Layered Manufacturing Techniques

Producing injection tooling with cooling channels of almost any form seems to be one of the most promising advantages of Layered Manufacturing Techniques (like Selective Laser Sintering). It could be efficiently exploited to achieve higher productivity or better quality parts in injection molding. Unfortunately, at the present time, the lack of data-processing tools to design optimal cooling systems still prevents us from fully benefiting from this new potential. The first objective of this paper is to present a methodology for the optimal design of cooling systems in three-dimensional injection molds. Our optimization process is based on a finite element model of the mold and on the standard gradient method. In the second part of this paper, we compare a conventional mold and a mold equipped with a cooling system optimized by means of the proposed methodology. The comparison is carried out thanks to an appropriate protocol. The conclusion is that the optimization of the cooling system doubled the productivity of the mold.Mechanical Engineerin

Optimization of Powder Layer Density in Selective Laser Sintering

An important parameter for the overall quality of SLS parts is the density of powder layers before sintering. Previous studies have shownthatthe control of powder particle shape and size distribution can increase the density of non-packed powder beds. However, these studies concerned beds several orders of magnitude larger than the SLS layers. The purpose ofthis study. is to determine if,and to what extent, the density of thin powder layers can be ineteased. Experiments show that the density of thin layers increases from 53% to 63% when adding 30% fine powder to the coarse powder,/with a coarse-to-fine ratio of 1:10. Compared with the bulk experiments, this density improvement method is less efficient, because the particles do not arrange as efficiently, and the wall effects can become predominant.Mechanical Engineerin

Predicting Risks Of Invasion Of Caulerpa Species In Florida

Invasions of exotic species are one of the primary causes of biodiversity loss on our planet (National Research Council 1995). In the marine environment, all habitat types including estuaries, coral reefs, mud flats, and rocky intertidal shorelines have been impacted (e.g. Bertness et al. 2001). Recently, the topic of invasive species has caught the public\u27s attention. In particular, there is worldwide concern about the aquarium strain of the green alga Caulerpa taxifolia (Vahl) C. Agardh that was introduced to the Mediterranean Sea in 1984 from the Monaco Oceanographic Museum. Since that time, it has flourished in thousands of hectares of near-shore waters. More recently, C. taxifolia has invaded southern Californian and Australian waters. Since the waters of Florida are similar to the waters of the Mediterranean Sea and other invasive sites my study will focus on determining potential invasion locations in Florida. I will look at the present distribution of C. taxifolia - native strain in Florida as well as the distribution of the whole genus around the state. During this study, I address three questions: 1) What is the current distribution of Caulerpa spp. in Florida? 2) Can I predict the location of potential Caulerpa spp. invasions using a set of environmental parameters and correlate them to the occurrence of the algae with the support of Geographic Information System (GIS) maps? 3) Using the results of part two, is there an ecological preferred environment for one or all Caulerpa spp. in Florida? To answer these questions, I surveyed 24 areas in each of 6 zones chosen in a stratified manner along the Floridian coastline to evaluate the association of potential indicators Caulerpa. Latitude, presence or absence of seagrass beds, human population density, and proximity to marinas were chosen as the 4 parameters expected to correlate to Caulerpa occurrences. A logistic regression model assessing the association of Caulerpa occurrence with measured variables has been developed to predict current and future probabilities of Caulerpa spp. presence throughout the state. Fourteen different species of Caulerpa spp. were found in 26 of the 132 sites visited. There was a positive correlation between Caulerpa spp. and seagrass beds presence and proximity to marinas. There was a negative correlation with latitude and human population density. C. taxifolia aquarium strain wasn\u27t found. Percent correct for our model was of 61.5% for presence and 98.1% for absence. This prediction model will allow us to focus on particular areas for future surveys

Polizeigeschosse und ihre Deformation: Abhängigkeit von Geschwindigkeit und Schussdistanz

Zusammenfassung: In den Jahren 2001 bis 2007 ist bei den Polizeien der deutschen Bundesländer und bei den Polizeikorps der Schweiz die so genannte Polizeimunition eingeführt worden. Von dieser mit einem deformierenden Geschoss ausgerüsteten Munition verspricht man sich eine größere Wirksamkeit und wegen der begrenzten Durchschlagsleistung eine geringere Gefährdung unbeteiligter Personen. Bei geringerer Auftreffenergie deformiert sich jedoch das Geschoss weniger, die Wirksamkeit wird kleiner und die Eindringtiefe größer. In der hier vorgestellten Arbeit wurde die Abhängigkeit der Deformation und der Eindringtiefe in ballistische Seife von der Auftreffenergie für alle 4 gegenwärtig vorhandenen Polizeigeschosse untersucht. Bereits bei Schussdistanzen von 25-30m ist mit einer verminderten Wirksamkeit zu rechnen. Bei einer viel gebrauchten Waffe kann zudem die Mündungsenergie so stark reduziert sein, dass sich bereits bei kurzen Schussdistanzen die Geschosse nicht mehr erwartungsgemäß deformiere

Dynamic obstacle avoidance for real-time character animation

This paper proposes a novel method to control virtual characters in dynamic environments. A virtual character is animated by a locomotion and jumping engine, enabling production of continuous parameterized motions. At any time during runtime, flat obstacles (e.g. a puddle of water) can be created and placed in front of a character. The method first decides whether the character is able to get around or jump over the obstacle. Then the motion parameters are accordingly modified. The transition from locomotion to jump is performed with an improved motion blending technique. While traditional blending approaches let the user choose the transition time and duration manually, our approach automatically controls transitions between motion patterns whose parameters are not known in advance. In addition, according to the animation context, blending operations are executed during a precise period of time to preserve specific physical properties. This ensures coherent movements over the parameter space of the original input motions. The initial locomotion type and speed are smoothly varied with respect to the required jump type and length. This variation is carefully computed in order to place the take-off foot as close to the created obstacle as possibl

Robust on-line adaptive footplant detection and enforcement for locomotion

A common problem in virtual character computer animation concerns the preservation of the basic foot-floor constraint (or footplant), consisting in detecting it before enforcing it. This paper describes a system capable of generating motion while continuously preserving the footplants for a real-time, dynamically evolving context. This system introduces a constraint detection method that improves classical techniques by adaptively selecting threshold values according to motion type and quality. The footplants are then enforced using a numerical inverse kinematics solver. As opposed to previous approaches, we define the footplant by attaching to it two effectors whose position at the beginning of the constraint can be modified, in order to place the foot on the ground, for example. However, the corrected posture at the constraint beginning is needed before it starts to ensure smoothness between the unconstrained and constrained states. We, therefore, present a new approach based on motion anticipation, which computes animation postures in advance, according to time-evolving motion parameters, such as locomotion speed and type. We illustrate our on-line approach with continuously modified locomotion patterns, and demonstrate its ability to correct motion artifacts, such as foot sliding, to change the constraint position and to modify from a straight to a curved walk motio

On-line locomotion synthesis for virtual humans

Ever since the development of Computer Graphics in the industrial and academic worlds in the seventies, public knowledge and expertise have grown in a tremendous way, notably because of the increasing fascination for Computer Animation. This specific field of Computer Graphics gathers numerous techniques, especially for the animation of characters or virtual humans in movies and video games. To create such high-fidelity animations, a particular interest has been dedicated to motion capture, a technology which allows to record the 3D movement of a live performer. The resulting realism motion is convincing. However, this technique offers little control to animators, as the recorded motion can only be played back. Recently, many advances based on motion capture have been published, concerning slight but precise modifications of an original motion or the parameterization of large motion databases. The challenge consists in combining motion realism with an intuitive on-line motion control, while preserving real-time performances. In the first part of this thesis, we would like to add a brick in the wall of motion parameterization techniques based on motion capture, by introducing a generic motion modeling for locomotion and jump activities. For this purpose, we simplify the motion representation using a statistical method in order to facilitate the elaboration of an efficient parametric model. This model is structured in hierarchical levels, allowing an intuitive motion synthesis with high-level parameters. In addition, we present a space and time normalization process to adapt our model to characters of various sizes. In the second part, we integrate this motion modeling in an animation engine, thus allowing for the generation of a continuous stream of motion for virtual humans. We provide two additional tools to improve the flexibility of our engine. Based on the concept of motion anticipation, we first introduce an on-line method for detecting and enforcing foot-ground constraints. Hence, a straight line walking motion can be smoothly modified to a curved one. Secondly, we propose an approach for the automatic and coherent synthesis of transitions from locomotion to jump (and inversely) motions, by taking into account their respective properties. Finally, we consider the interaction of a virtual human with its environment. Given initial and final conditions set on the locomotion speed and foot positions, we propose a method which computes the corresponding trajectory. To illustrate this method, we propose a case study which mirrors as closely as possible the behavior of a human confronted with an obstacle: at any time, obstacles may be interactively created in front of a moving virtual human. Our method computes a trajectory allowing the virtual human to precisely jump over the obstacle in an on-line manner

La relation du texte à l’image dans l’Hortus sanitatis et les traités du milieu du XVIe siècle : quelques points de comparaison

Pour les historiens des sciences, les herbarii et les autres éditions incunables des premiers traités botaniques ou de simples n’ont guère d’autre intérêt que celui de préfigurer les histoires naturelles du milieu du XVIe siècle, elles-mêmes annonciatrices des ouvrages pré-scientifiques des deux siècles suivants. Maladroits, naïfs, incomplets, les épithètes péjoratives ne manquent pas pour déconsidérer les premiers livres de simples imprimés, censés précéder et annoncer une rupture épistémologique, concrétisée par les travaux des médecins naturalistes comme Fuchs, Gesner, Belon, Rondelet, Aldrovandi et leurs collègues. Prêter attention à ces deux familles d’ouvrages du point de vue non de la discontinuité, mais de la filiation et de la comparaison devrait permettre de réévaluer plus judicieusement l’évolution de l’histoire naturelle à partir de la Renaissance, sans préjugé ni anachronisme. Le travail d’analyse des incunables de botanique et d’histoire naturelle est en cours depuis quelques décennies et porte tant sur l’analyse des textes que sur celle des gravures nombreuses qui les accompagnent. Pourtant, dans la mesure où les traités du XVIe siècle ont été considérés comme radicalement distincts de leurs pendants incunables, peu de liens ont été établis entre ces deux groupes d’ouvrages. C’est cette lacune que je me propose de combler – très partiellement – en examinant quels liens unissent les textes et les illustrations dans les deux catégories de livres.According to historians of sciences, herbarii and other incunabula of the first botanical treatises have no other interest than announce treatises of mid-XVIth century that would announce, in their turn, pre-scientific books of the two following centuries. Ackward, naive, incomplete are some of depreciative judgments people passed on these books, and one usually thinks they just come before and announce the epistemological rupture that doctors like Fuchs, Rondelet, Gesner, Belon, Aldrovandi and others would realize in their works. In this article, though, we don’t intend to consider both group of works separatly, but we’d like to point at the way they are linked, both in texts and pictures, without anachronism nor prejudices

An innovative method to build support structures with a pulsed laser in the selective laser melting process

In selective laser melting machines, continuous laser are usually used to melt the powder. The support structures, which are inevitable when dealing with elaborated pieces, necessitate a complex design by CAD in order to be easily removed. This paper propose an innovative laser manufacturing method by combining pulsed and continuous modes of radiation. Continuous radiations are used for the object-to-build itself, in order to guarantee the requested mechanical properties. Pulsed radiations are used to build the support structures. The resulting support structures have sufficient mechanical properties to withstand the deposition system and to evacuate heat, and are easy to remove from the denser parts. This building method reduces drastically time to market since the same laser can be used in two modes and because pulsed radiation allows very high scanning speed with high power during the building of support structure